DL11-W - UART and new baudrates

Selecting baudrates

After replacing 74LS86 at E27, the baud rate selection logic on the DL11-W has not changed ... you still need good nerves to select a baud rate. There's absolutely no logic in the switch layout! Here is the new switch-setting-table: 

Possible show stopper: the UART

The UART on DL11-W is DEC 19-10459-01. There are a lot of replacement types:

• SMC: COM2017
• AMI: S1883,
• GI: AY-5-1013,
• TI: TMS6011,
• WD: TR1602

Most of these chips can only reach 19200 baud, some even break at ca. 10kBaud.
The AY-5-1013A is capable of 40KBaud and could reach 38400, but is not used on DL11-W.

So bad news are: until you shop, 19200 is the limit.

The good news are: After I replaced my DEC UART (date code 1978) with a AY-5-1013A (1987), 38400 baud are working!

Test

A self test is mandatory, since the 3% speed difference may be intolerable, and the old UART may not be able to communicate well at 19200 or 38400 baud .
Just transmit and receive a lot of characters and check them :-)

You can run one of the DEC diagnostics. "ZDLDI0" on the XXDP2.5 RL02 disk seems to be the best test. A H325 loop back adapter is required.

PDP11GUI is also a good idea:

1. Use the "communication self test" function of the "Read/Write disk images windows".
2. Choose any non-MSCP disk , click "reset and open disk". A driver is loaded, but no contact to the disk drive is required.
3. On the bottom of the window is the self test panel.
4. Choose a test strategy ("count up" is fine), and a repeat count (1 is good for the first time) and click "Test". A block of compressed data is sent to the driver and echoed back.
5. Since there's parity check in the protocol, you quickly see wether the RS232 port is reliable.